The present invention relates to devices for penetrating the skin to extract blood or other fluids, and more particularly, to a skin-pricking device having multiple penetrating tips.
Medical tests that require a small volume of blood are well known. For example, home test kits for measuring blood sugar levels are utilized by diabetics. These test kits require that a drop of blood be placed on a test strip that is then inserted into a measurement apparatus that displays the glucose concentration in the blood sample. To obtain the drop of blood, the user is supplied with a lancet device, which makes a skin prick, typically in the user""s finger. It would be advantageous to minimize the physical discomfort associated with this skin prick to obtain an amount of blood adequate for the test.
To successfully obtain blood, a piercing device must traverse the skin""s various layers to reach the blood vasculature. Human skin is composed of a tough, keratinized squamous epithelium. The outermost layer of skin is known as the epidermis (0.07 to 0.12 mm thick), and has its own distinct layers: stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. (For a review about skin, see Tortora and Anagnostakos xe2x80x9cPrinciples of anatomy and Physiology,xe2x80x9d Harper and Row 1981). Underneath the epidermis is the dermis, which is 1 to 2 mm thick. Because of its varying elasticity and the thickness due to the cellular structure and anatomical locations, the force necessary for penetrating the epidermis to access the vascular beds within the dermis layer will vary. It has been reported that skin tension is the greatest in the areas where the epidermal elastic keratinous fibers are dense, particularly in regions where the skin is thick, such as is found in the epigastric (stomach) regions.
The amount of force necessary to penetrate the skin surface will depend on the force applied normal to the surface of the skin needed to exceed the rupture strength. There exists an elastic range within which the degree of deflection corresponds directly with the applied force (skin depression). When the rupture limit is exceeded, a non-linear response by the skin (otherwise known as the inelastic response) occurs, corresponding to the further stretching of the skin at the point of application prior to rupture. The applied force reaches a maximum when the skin ruptures, resulting in the penetration of the object into the skin. The capillary bed under the dermis is approximately 300 to 750 microns below the outer surface of the skin in the areas of the fingers, the forearms and the abdomen. Bleeding occurs when the penetration of the object reaches the capillary bed.
Pain in blood sampling due to the skin being pierced is thought to be generated, in part, through pressure waves that are built up at the site of puncture. Many factors affect the pain sensation. Minimizing the incision angle of penetration, and hence the pressure wave buildup, would help reduce the pain sensation on sampling. In addition to the force required to penetrate the skin, the depth of penetration affects the sensation of pain as well. Optimizing these factors to reduce patient discomfort will encourage compliance to self test, for example, for diabetic self-monitoring.
A successful method to minimize pain generation due to skin puncture by a needle, pin or lancet, would be to minimize the area over which the puncture occurs. This can be achieved by miniaturizing the needle or lancet, provided the force applied to create the wound is small. The smaller the needle, the less force is required to puncture the skin, and fewer nerve endings are stimulated by the cut. Unfortunately, there is a lower limit on the size of the needle, since smaller needle pricks produce less blood than larger needle pricks, and there is a minimum amount of blood that must be extracted for any given test or analytical procedure.
Certain lancets have been used for special purposes. For example, needle devices with multiple needles have been used in a Hear Test (tuberculin test), as was described in U.S. Pat. No. 5,611,809 (Marshall et al.), to carry a substance smeared on the skin surface into the blood vessels. However, this device is aimed specifically at injecting a sufficient amount of immunogen into the skin. The multiple needles provide a larger surface area to deliver a larger dose of the substance into the puncture wounds than a single larger needle. This design was seen to be generally applicable to vaccination, and is very similar to U.S. Pat. No. 4,109,655 (Chacornac), which describes a multi-penetration vaccination apparatus. The Chacornac vaccination apparatus has concentric sleeves with points for skin penetration. The points are dipped into a vaccine, which is then delivered into the skin by the points.
In the prior vaccination technology, when multiple needle pricks are used on a patient, the patient perceives the multiple needle pricks. For vaccination, despite the discomfort, being pricked a number of times and at a number of different locations is acceptable. These techniques are intended for carrying vaccines into tissue, not for withdrawing or extracting fluid from the pricked tissue.
For fluid (e.g. blood) sampling, there is still a need for a technique that can extract an adequate amount of blood with minimal discomfort to the patient.
The present invention provides a technique for extracting blood from the skin of a user with reduced discomfort. In one aspect, a device for puncturing the skin of a patient is provided. The device includes two or more protrusions. Each protrusion punctures the skin when it is pressed against the skin. At least two, preferably all, of the protrusions are arranged such that a first protrusion punctures the skin at a location equal or less than a predetermined distance from a neighboring protrusion. The distance is chosen such that the patient perceives a single puncture when the first and the neighboring protrusions, and preferably all of the protrusions, puncture the skin. In one embodiment of the invention, the device includes a base assembly that applies a lateral force to the skin when the base assembly is applied against the skin, thereby causing the skin to be taut. In this embodiment, the protrusions are pressed into the skin as the base assembly is pressed against the skin.
The present invention provides a technique by which a user perceives a single puncture when sampling blood when in fact two or more punctures are administered. This technique thus reduces the discomfort to the user while ensuring adequate sampling of fluid (e.g., blood) from the puncture wounds. To this end, the present invention provides an improved lancet device having multiple lancets with at least two, preferably all, of the lancets being less than or equal to the critical distance apart from one another.
Further, the present invention provides better control on the depth of penetration of the lancet by increasing the tautness of the skin for the puncture to occur. This increase of tautness can be implemented by pushing the skin with a lateral force component at locations surrounding a central site where lancet penetration occurs. The increase in tautness reduces the uncertainty of the depth of penetration by the lancet into the skin as a result of the amount of imperfections in the skin, such as wrinkles. Further, in another embodiment, varying the length of the protrusions, for example, having longer protrusion on the inside, accomplishes a more uniform penetration and therefore better fluid sampling by the protrusions.